Immanuel Velikovsky's Worlds in Collision was published in April 1950 by New York's Macmillan. I can remember reading the Dell edition in the late 1960s. The copy below is the 10th printing from August 1972. The first, not surprisingly, is May 1967, the Summer of Love. Velikovsky's anti-(science) establishment text fit right in.
I've just read the newly published The Pseudoscience Wars (Chicago: University of Chicago Press) - highly recommend. Fascinating and well written.
What other books might have been found in a bookstore or on a newsstand in April 1950? Here are three, the first two in Canada, the last in the US.
Dell 9702 - August 1972 (10th printing)
Dell 9702 back
Harlequin 42 - April 1950
News Stand Library 103 - April 1950
News Stand Library 23A (with DJ) - April 1950